1. Field of the Invention
The present invention relates to a charge pump apparatus, in particular, to a charge pump apparatus having dynamic feedback control capability.
2. Description of Related Art
An electronic circuit often needs various power supply voltages of different levels, and thus a charge pump circuit is usually configured to use the existing power supply voltage to generate various power supply voltages of different levels. The charge pump circuit generates the voltages of different levels by boosting (or bucking) the input voltage with a predetermined multiple. Therefore, the levels of the output voltage of the charge pump circuit are closely related to the input voltage. However, in order to extend the applications of the charge pump circuit in various environments (i.e., the input voltage is uncertain when the charge pump circuit is designed), for generating the expected output voltages, usually, a voltage regulator circuit is used to first regulate the levels of the output voltage to a rated voltage, and the charge pump is then used to generate a rated output voltage.
FIG. 1 is a circuit diagram of a conventional charge pump. A capacitor C, a switch 102, a switch 103, a switch 104, and a switch 105 form a charge pump. A transistor T1, an operational amplifier 101, a resistor R1, and a resistor R2 form a voltage regulator circuit with a negative feedback. The voltage regulator circuit receives a system voltage VCC, and regulates the system voltage VCC to an input voltage Vin1. In a first duty cycle of the charge pump, the switches 102 and 105 are short-circuited, and the switches 103 and 104 are open-circuited. At this time, the input voltage Vin1 charges the capacitor C, such that the capacitor C has a potential equal to that of the input voltage Vin1. In a second duty cycle of the charge pump, the switches 103 and 104 are short-circuited, and the switches 102 and 105 are open-circuited, such that one end of the capacitor C is disconnected from the ground but is connected to the input voltage Vin1 (i.e., changes from 0V to Vin1), and the potential at other end of the capacitor C rises Vin1 to 2Vin1. Therefore, the output voltage Vout1 that is twice that of the input voltage Vin1, is obtained.
The conventional charge pump may provide the voltage twice that of the input voltage Vin1, but when current at the output end of the charge pump changes due to the load variation, the voltage regulator circuit cannot detect and regulate the input voltage Vin1 in real time according to the change of the output current, such that the output voltage Vout1 generates a serious ripple problem along with the change of the load current. In order to eliminate the ripple, the charge pump has its input end directly coupled to the system voltage, and its output end coupled to a voltage regulator having a regulator capacitor. However, this solution causes the load problem of the voltage regulator, and the added regulator capacitor also increase the burden of cost, such that the functions of the charge pump cannot be fully exerted.